Abstract

The occurrence of lizardite-1T and lizardite-2H1 from Coli, Italy, is reported. The two polytypes can be identified by their morphology. The 1T polytype occurs as truncated trigonal pyramids and the 2H1 polytype as truncated hexagonal pyramids or hexagonal plates. Lizardite-1T has the composition (Mg2.82Fe0.07Al0.09)(Si1.94Al0.06)O5(OH)4, and lizardite-2H1 has the composition (Mg2.83Fe0.05Al0.10)(Si1.93Al0.07)O5(OH)4.

Unit-cell parameters are a = 5.325(5), c = 7.259(7) Å, space group P3lm, and a = 5.318(4), c = 14.541(7) Å, space group P63cm for the 1T and 2H1 polytypes, respectively.

The crystal structures of the two polytypes have been refined to R = 0.074 and 0.024 (1T and 2H1, respectively). Whereas the tetrahedral-octahedral layer exhibits negative ditrigonalization in the 1T structure (α = -1.7°), positive distortion (α = +6.4°) occurs in the 2H1 structure. This pattern fits the existing predictions about the layer configurations within the different polytypes of lizardite.

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